The present invention relates to fiber-optic communications networks, and more particularly, to optical network equipment such as optical amplifiers with the ability to control gain transients and to make gain adjustments to compensate for drift effects.
Fiber-optic networks are used to support voice and data communications. In optical networks that use wavelength division multiplexing, multiple wavelengths of light are used to support multiple communications channels on a single fiber.
Optical amplifiers are used in fiber-optic networks to amplify optical signals. For example, optical amplifiers may be used to amplify optical data signals that have been subject to attenuation over fiber-optic paths. A typical amplifier may include erbium-doped fiber coils that are pumped with diode lasers. Raman amplifiers have also been investigated. Discrete Raman amplifiers may use coils of dispersion-compensating fiber to provide Raman gain. Distributed Raman amplifiers provide gain in the transmission fiber spans that are used to carry optical data signals between network nodes.
It is an object of the present invention to provide optical network equipment such as optical amplifiers that suppress gain transients due to fluctuations in input power and that compensate for drift effects due to temperature fluctuations or aging.
This and other objects of the invention are accomplished in accordance with the present invention by providing optical amplifiers and other optical network equipment for use in handling optical data signals in a signal band in fiber-optic communications links. The fiber-optic communications links may carry a number of wavelength-division multiplexing channels each having a different corresponding wavelength. The equipment may include optical gain stages for providing optical gain for the optical signals. The gain stages may be based on optically-pumped fiber. Laser diode pump lasers may be used to pump the fiber.
Sudden fluctuations in the input power of the optical data signals may result from changes in the number of channels being carried in the signal band. Optical taps and monitors may be used in the equipment to make power measurements that reveal these fluctuations. A control unit may adjust the pump power provided by the laser diodes in real time based on the power measurements to ensure that the gain in the optically pumped fiber does not experience significant gain transients.
Slower fluctuations in the input of the optical data signals may result from changes in the temperature of the transmission fiber in a given span in the fiber-optic communications link or changes in the temperature of other optical components in the system. Slower changes may also result from aging effects. Because of temperature-induced and aging-induced drift effects, the input power to the equipment in the link may not be stable. As a result, the output power of the equipment may not be stable unless the gain level of the equipment is adjusted slightly to compensate.
To avoid conflicts with the transient control capabilities of the equipment, the control unit may automatically determine which power changes are fast changes that require real-time pump power adjustments to prevent gain transients and which changes are slow changes that require gain level adjustments to ensure a constant output power.
Further features of the invention and its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments.